The benefits of sensing parameters such as pressure, flowrate and temperature around a wellhead and associated flowlines and chokes are well known. Such sensors are routinely deployed in (for example) high value oil and gas wells, particularly offshore wells and land wells close to power and communications infrastructure.
However, a significant percentage of the world's oil and gas reserves are produced from wells completely remote from mains power or communications infrastructure. At present, such wells are largely unmonitored, or are only instrumented with mechanical gauges. They are visited occasionally by oil company personnel. The lack of real-time monitoring means that problems with the well can go unnoticed for some time, causing deferred or lost production. The lack of a reasonable quality database on the well means that reservoir analysis is hampered, and the reservoir reserves are more uncertain.
The desirability of real-time sensing even where there is no power or communications infrastructure is thus a highly specialised requirement applicable to oil and gas fields. In contrast, sensors deployed for industrial process control measurements have power available relatively close to the sensor, as industrial processes requires power, in contrast to a free flowing oil or gas well.
Various solutions have been proposed to monitor wells in remote oil and gas fields. Battery powered data loggers have been deployed that record measurements from time to time. This data can then be manually collected later. While providing a more regular electronic data record of the parameters associated with the well, the lack of real-time reporting is still a drawback along with the requirement to visit the wellsite at intervals for data collection.
Point to multi-point radio solutions have been implemented. In these systems the sensors around the wellsite are cabled to a wellsite radio transmitter. This transmitter then communicates with a remote central receiving station where the data is gathered for the field. The drawbacks of these systems are the cost and vulnerability of the wellsite cabling, and the lack of resilience and range of a point to multi-point radio system. Repeater stations may be deployed to increase range, but the lack of resilience of the system, and the requirement for careful configuration during installation remain.
Radio systems have also been deployed where each sensor incorporates a transmitter, hence eliminating the wellsite cabling. As the sensors are located close to the ground by the wellhead, the radio range of such sensors is limited. Typically such sensors communicate with a local wellsite receiver that then forwards the information on via satellite modem, GPRS modem, or a point to point radio system. Satellite and GPRS systems (when GPRS service is available) incur ongoing call charges that either substantially increase the running cost of the system, or force a very slow data collection rate to minimise call charges. Conventional radio systems incur the same problems of inflexibility, lack of resilience and requirement for field configuration that have already been mentioned.